Take advantage of atmospheric depth
Atmospheric depth is an important part of any composition because it separates the fore-, mid- and background. A distinct separation of the three planes increases the readability of your image, which in turn increases the visual impact of your image. Elements that are further away from the viewer become less detailed as a result of different weather conditions, such as fog, haze, humidity and pollution. The background plane will usually feature less saturation, contrast and details. I often use a soft Cloud brush in Photoshop to mimic this effect.